1. Field of the Invention
The present invention relates generally to radio communication apparatus, such as a mobile radio telephone apparatus, and more particularly, to improvements in a radio communication apparatus which has a signal transmitting portion operative to cause a transmissible signal, which is produced by modulating a carrier with a signal to communicate, to be subjected to power amplification and then to transmit the transmissible signal having been subjected to the power amplification. Still more particularly, this invention relates to a controlled fan cooling system for the radio telephone apparatus of the type disclosed wherein the cooling system is responsive to an operative condition or to the temperature of the power amplifier.
2. Description of the Prior Art
In a public mobile telephone system which is one of a plurality of mobile radio communication systems, communications between an automobile on which a mobile radio telephone apparatus is mounted and an ordinary telephone subscriber or between automobiles each provided with the mobile radio telephone apparatus are carried out through a particular local base station. A radio communication apparatus constituting the mobile radio telephone apparatus used in the public mobile telephone system is operative to transmit and receive a speech signal selectively. In transmission of the speech signal by the mobile radio telephone apparatus, a transmissible signal is produced by, for example, frequency-modulating a predetermined carrier with the speech signal and then subjecting the modulated carrier to power amplification to be transmitted. Therefore, the radio communication apparatus constituting the mobile radio telephone apparatus is required to have a signal transmitting portion including a frequency-modulator for performing frequency-modulation in which the speech signal provides the part of a modulating signal to produce the transmissible signal and a power amplifier for causing the transmissible signal obtained from the frequency-modulator to be subjected to power amplification in advance of transmission.
The signal transmitting portion of the radio communication apparatus constituting the mobile radio telephone apparatus, which is provided with the power amplifier as described above, is put in a heat generating condition with a heat source constituted by the power amplifier when the power amplifier is in operation. Accordingly, in the previously-proposed radio communication apparatus constituting the mobile radio telephone apparatus, a chassis used in the signal transmitting portion of the apparatus is provided in the form of an aluminum alloy die-casting so that heat generated by the power amplifier is efficiently radiated through the chassis. Furthermore, many heat sink members are disposed around the power amplifier.
However, in the case of such previously-proposed radio communication apparatus, it is feared that a rise in temperature of the signal transmitting portion including the power amplifier is not sufficiently suppressed even by means of using the chassis provided in the form of an aluminum alloy die-casting and by disposing many heat sink members around the power amplifier. Therefore, a problem occurs in that the transmission of the transmissible signal is carried out under an unstable operating condition of the signal transmitting portion.